Composed of glands that secrete hormones into the circulatory system.

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Characteristics of theEndocrine System

• Composed of glands that secrete hormones into the
  circulatory system.
• Hormones are secreted in minute amounts into the
  interstitial space.
• Hormones eventually enter the circulatory system
  and arrive at specific target tissues.

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Characteristics of theEndocrine System

• Functions are similar to the nervous system.
• Differences
• Amplitude-modulated vs. Frequency-modulated
• Response of target tissue to hormones is usually
  slower and of longer duration than that to
  neurons.

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Chemical Structureof Hormones

• Peptides Proteins Most hormones are either
  peptides or proteins and are usually referred to
  as peptide hormones.
• Amines Amine hormones are derivatives of the
  amino acid tyrosine. 
• Lipids Steroids Steroid hormones are produced
  by the adrenal cortex and the gonads. 

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Control ofSecretion Rates

• Hormones control the rates of many activities in
  the body.
• The rate at which each hormone is secreted is
  controlled by a negative feedback mechanism.
• Three major patterns of regulation
• Non-hormone substance (e.g. insulin)

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Control ofSecretion Rates

• Hormones control the rates of many activities in
  the body.
• The rate at which each hormone is secreted is
  controlled by a negative feedback mechanism.
• Three major patterns of regulation
• Non-hormone substance (e.g. insulin)
• Stimulation by the nervous system (e.g.
  epinephrine)

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Control ofSecretion Rates

• Hormones control the rates of many activities in
  the body.
• The rate at which each hormone is secreted is
  controlled by a negative feedback mechanism.
• Three major patterns of regulation
• Non-hormone substance (e.g. insulin)
• Stimulation by the nervous system (e.g.
  epinephrine)
• Hormone from another endocrine tissue (e.g. TRH,
  TSH)

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Transport and Distributionin the Body

• Hormones are dissolved in the blood plasma and
  transported in free form or bound to a protein
  carrier.
• As a result, hormones can be distributed
  throughout the body relatively quickly.
• Hormones diffuse from the capillary to the
  interstitial space.

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Transport and Distributionin the Body

• Lipid-soluble hormones diffuse through the walls
  of all capillaries.
• Water-soluble hormones must pass through pores.

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Metabolism and Excretion

• Hormones are only active in the body for a
  certain time because they are destroyed and
  eliminated shortly after they are secreted.
• Half-life length of time that it takes to
  eliminate half of the total amount of hormone
  that was secreted.

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Metabolism and Excretion

• Water-soluble hormones have relatively short
  half-lives because they are rapidly broken down
  by enzymes.
• These hormones normally have concentrations that
  increase and decrease rapidly in the blood.
• They generally regulate activities that have a
  quick onset and a short duration.

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Metabolism and Excretion

• Lipid-soluble hormones are usually bound to
  protein carriers.
• The rate at which these hormones are broken down
  is greatly reduced.
• Therefore, these hormones have longer half-lives.

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Metabolism and Excretion

• Hormones are removed from the blood in four ways.
• Excretion (kidney, liver)
• Metabolism (enzymes)
• Active transport (actively transported into cells
  and secreted again)
• Conjugation (attach water-soluble molecules to
  hormone and then excreted by kidney or liver).

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Interaction of Hormoneswith Their Target Tissues.

• Hormones only interact with cells that have
  binding sites that are specific for the
  particular hormone.

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Classes ofHormone Receptors.

• Hormones can be placed into one of two major
  categories.
• Hormones that cannot pass through the plasma
  membrane.
• Hormones that can pass through the plasma
  membrane.
• As a result, hormone receptors need to be located
  in different locations.

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Membrane-BoundHormone Receptors.

• Some receptors are located in the membrane of the
  target tissue.
• After a hormone binds to the receptor, the
  receptor initiates events that lead to a
  response.
• Some receptors alter membrane permeability.

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Membrane-BoundHormone Receptors.

• Some receptors are located in the membrane of the
  target tissue.
• After a hormone binds to the receptor, the
  receptor initiates events that lead to a
  response.
• Some receptors alter membrane permeability.
• Some receptors activate G proteins.

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Membrane-BoundHormone Receptors.

• Some receptors are located in the membrane of the
  target tissue.
• After a hormone binds to the receptor, the
  receptor initiates events that lead to a
  response.
• Some receptors alter membrane permeability.
• Some receptors activate G proteins.
• Some receptors alter intracellular enzyme
  activity.

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IntracellularHormone Receptors.

• Some receptors are located in the target cell.
• They are located either in the cytoplasm or in
  the nucleus of the target cell.
• Once the hormone binds to the receptor, the
  effects of the hormone take place.

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Functions of theEndocrine System

• Metabolism and tissue maturation.
• Ion regulation.
• Water balance.
• Immune system regulation.
• Heart rate and blood pressure regulation.
• Control of blood glucose and other nutrients.
• Control of reproductive functions.
• Uterine contractions and milk release.

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Pituitary Glandand Hypothalamus

• Pituitary gland is responsible for secreting nine
  hormones.
• Hypothalamus regulates the pituitary glands
  secretions.

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Pituitary Gland

• Divided into a posterior and anterior portion.
• Posterior pituitary is also known as the
  neurohypophysis, because it is continuous with
  the brain.
• Anterior pituitary is also known as the
  adenohypophysis, because it acts more as a gland.

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Relationship of thePituitary Gland to the Brain

• The hypothalamus and the anterior pituitary are
  connected to each other via blood vessels.
• Hypothalamus produces neurohormones that travel
  to the anterior pituitary via the blood.
• Neurohormones then leave the blood and act on the
  cells in the anterior pituitary.

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Relationship of thePituitary Gland to the Brain

• Some neurohormones acts as releasing hormones and
  others act as inhibiting hormones.
• This is how the hypothalamus controls the
  anterior pituitary gland.
• See table 18.1 for a complete description of the
  hormones of the hypothalamus.

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Relationship of thePituitary Gland to the Brain

• There are no blood vessels that connect the
  hypothalamus to the posterior pituitary.
• Instead, neurohormones produced in the
  hypothalamus travel to the posterior pituitary
  via axons.

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Hormones of thePosterior Pituitary

• Posterior pituitary stores and secretes two
  polypeptide hormones
• Antidiuretic hormone (ADH)
• Oxytocin

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Antidiuretic Hormone (ADH)

• ADH is synthesized in the hypothalamus and
  transported to the posterior pituitary.
• ADH is then released into the circulatory system
  and carried to the primary target tissue in the
  kidney.
• ADH promotes water retention and reduces urine
  volume.

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Hormones of theAnterior Pituitary

• Anterior pituitary hormones are called tropic
  hormones.

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Hormones of theAnterior Pituitary

• Anterior pituitary hormones are called tropic
  hormones.
• We will only address one of the many tropic
  hormones
• Thyroid-stimulating hormone

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Thyroid-stimulatingHormone (TSH)

• TSH is also known as thyrotropin.
• Stimulates the synthesis and secretion of thyroid
  hormones from the thyroid gland.
• TSH secretion is controlled by TRH from the
  hypothalamus.

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Thyroid Gland Hormones

• Thyroid hormones exist in two forms
• Triiodothyronine (T3)
• Tetraiodothyronine (T4) (also called thyroxine)
• Approx. 90 T4 and 10 T3 secreted.

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Thyroid Gland Hormones

• Thyroid hormones are transported in the blood in
  combination with plasma proteins.
• Approx. 70-75 of T3 T4 are bound to
  thyroxin-binding globulin (TBG).
• 20-30 are bound to other plasma proteins.
• Therefore, high half-life.

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Thyroid Gland Hormones

• Thyroid hormones diffuse through the target cell
  membrane.
• Bind to receptors in the nucleus.
• Thyroid hormones affect nearly every tissue in
  the body.
• Factors such as metabolism, growth, and
  maturation are affected.

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Regulation ofThyroid Hormone Secretion

• TRH TSH help control thyroid hormone levels.
• Exposure to stress and cold increases TRH.
• Prolonged fasting decreases TRH.

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Regulation ofThyroid Hormone Secretion

• TRH TSH help control thyroid hormone levels.
• Exposure to stress and cold increases TRH.
• Prolonged fasting decreases TRH.
• Abnormal thyroid conditions are listed in Table
  18.5

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The Adrenal Glands

• Located atop the kidneys.
• Composed of an inner medulla and an outer cortex.

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The Adrenal Medulla

• Two major hormones
• Epinephrine (80)
• Norepinephrine (20)
• See Table 18.7 for structure, target tissue, and
  response.

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The Adrenal Cortex

• All hormones are steroids.
• Lipid soluble and are carried in the plasma by
  protein carriers.
• Three hormone types
• Mineralocorticoids (e.g. aldosterone)
• Glucocorticoids (e.g. cortisol)
• Androgens

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The Adrenal Cortex

• Adrenocorticotropin-releasing hormone (ACTH) is
  necessary to maintain the sensory activity of the
  adrenal cortex.
• Corticotropin-releasing hormone (CRH) is released
  from the hypothalamus and stimulates the anterior
  pituitary to secrete ACTH.

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The Adrenal Cortex

• Table 18.9 outlines the abnormalities associated
  with hypersecretion and hyposecretion of adrenal
  hormones.

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The Adrenal Cortex

• Table 18.9 outlines the abnormalities associated
  with hypersecretion and hyposecretion of adrenal
  hormones.
• Predict 7

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Predict 7

• Cortisone, a drug similar to cortisol, is
  sometimes given to people who have severe
  allergies or extensive inflammation or who suffer
  from autoimmune diseases. Taking this substance
  chronically can damage the adrenal cortex.
• Explain how this damage can occur.

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The Adrenal Cortex

• Table 18.9 outlines the abnormalities associated
  with hypersecretion and hyposecretion of adrenal
  hormones.
• Predict 7
• Clinical Focus Stress (page 621 633)

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Effects of Aging

• What happens to the endocrine system when we get
  old?
• Endocrine glands differ in how they respond to
  the aging process.
• Some experience a gradual decrease in secretion
  while others are not affected to a great degree.

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Effects of Aging - Growth Hormone -

• There is a decrease in growth hormone (GH).
• Decrease is greater in people who do not
  exercise.
• Decreases in GH may explain a gradual decrease in
  lean-body mass in these people.

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Effects of Aging - Melatonin -

• Melatonin decreases in aging people.
• May influence sleeping patterns.
• May also affect the patterns of other hormones
  like GH and testosterone.

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Effects of Aging - Thyroid Hormone -

• Decreases slightly with increasing age.
• Age-related damage to the thyroid gland may also
  occur.

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Effects of Aging - Insulin -

• There does not appear to be a age-related
  decrease in the ability to maintain blood glucose
  levels.
• However, there is an age-related tendency to
  develop Type II diabetes.

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Hormonelike Substances

• Autocrine chemical signals are released from
  cells in a local area and influence activity of
  the same cell type.
• Paracrine chemical signals are produced by a wide
  variety of tissues and secreted into tissue
  spaces.

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Hormonelike Substances

• Autocrine and paracrine signals are not like
  hormone signals.
• They are not secreted by endocrine glands.
• They act locally not systemically.
• They are also not completely understood

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Autocrine Chemical Signals

• Autocrine chemical signals include the chemical
  mediators of inflammation.
• Prostaglandins
• Thromboxanes
• Prostacyclins
• Leukotrienes
• Collectively known as eicosanoids.

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Autocrine Chemical Signals

• These products are released from injured cells.
• Responsible for initiating some of the symptoms
  of inflammation.
• Pain receptors are stimulated directly by
  prostaglandins.

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Prostaglandins

• Produced in all cells in the body except for red
  blood cells.
• Once prostaglandins enter the circulatory system,
  they are metabolized rapidly.
• They are synthesized from essential fatty acids
  (omega-3, omega-6).
• Ratio of omega-6omega-3 seems to be important in
  the synthesis of prostaglandins.

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Prostaglandins

• Anti-inflammatory drugs like asprin inhibit
  prostaglandin synthesis.
• Prostaglandins can both intensify or diminish
  inflammation and increase or decrease the
  clotting tendency of the blood.
• In order for the body to remain healthy, these
  two potentials must be properly balanced.

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Prostaglandins

• In simple terms prostaglandins derived from
  omega-6 fatty acids promote inflammation and
  blood clotting, while those derived from omega-3
  fatty acids oppose those effects.
• Remember that both are needed to maintain health.

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Prostaglandins

• Evidence suggests that our diet can affect this
  balance.
• The Western diet is deficient in omega-3 fatty
  acids.
• An ideal omega-6omega-3 ratio is between 11 and
  41.
• A typical American diet is between 201 and 401!

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Prostaglandins

• Essential fatty acid deficiency and
  omega-6omega-3 imbalance is linked with the
  following serious health conditions

Heart attack Cancer Insulin resistance Asthma
Lupus Schizophrenia Depression Stroke
Obesity Diabetes Arthritis Alzheimers Disease
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Prostaglandins

• Omega-3 sources
• Flaxseed oil
• Fish oil
• Flax seeds, hemp seeds
• Walnuts, walnut oil
• Salmon, herring, mackerel, sardines
• Soybeans, soybean oil

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Prostaglandins

• Omega-6 sources
• Corn oil
• Peanut oil
• Meat
• Poultry
• Safflower oil
• Sesame oil
• Sunflower oil